Glass-to-metal seals



Oct. 22, 1963 R. L. BREADNER 3,107,757

GLAss-To-METAL SEALS Filed oct. 50,1959

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, United States Patent Oiiiice 3', l 77 5 Patented ocr. 22, 1963 3,107,757 GLASS-TO-METAL SEALS l Robert Leonard Breadner, Harrow, England, assigner to The General Electric Company Limited, London, England Filed Oct. `30, 1959, Ser. No. 849,927 Claims priority, application Great Britain Nov. 5, 1958 v t 1 Claim. (Cl. 189--36.5)

that the glass tends to creep along the surface of the wire,

forming a meniscus which, after soliditication, is very fragile at its sharp edge. During subsequent handling of the seals cracks are liable to start at this sharp edge onilexureof the Wire or on exposure to thermal shock, and may then spread throughout the glass body, leading to failureof the seal.

Methods of reducing this -difliculty have been proposed in which sa flange formed on or carried by the wire abuts against or is embedded in the glass surface and an object of the present invention is to provide a further seal which may be used as an alternative to, or in some cases in conjunction with, these previously proposed seals.

A matched glassto-metal seal according to the present invention comprises a glass body, a metal wire hermetically sealed through the glass body, and a single metal sleeve closely surrounding the wire and extending through one surface of, and the greater pant of the way through, the glass body, vand sealed to the glass on both the inner and outer surfaces of the sleeve.

By closely surrounding is meant so spaced from the wire that the thickness of the cylindrical annulus of glass between the Wire and sleeve is small in comparison with the depth of penetration of the sleeve into the glass. Preferably also the thickness is also small compared with the minimum width of the'region of the glass lying outside the sleeve.

Preferably also the sleeve projects some way out of the glass so as to limit the extent to which the wire at or `very close to the glass surface at that side can be bent.

The metal components must, of course, be suitably matched to the glass as regards their thermal expansion coeliicients, the closeness of the matching required depending, of course, on the ductility of the metal, on the dimensions of the parts of the seal, and on the type of seal, as is well known.

The seal will, in general, be completed by sealing the glass body in turn, or simultaneously, into an aperture in a further body, which may be of metal, ceramic or glass, whose thermal expansion coeiiicient must also be suitably matched to that of the glass.

With a seal constructed in accordance 'with the inventhe metal ywire is provided with a flange embedded at the other surface ofthe glass body and the embedded end of the sleeve abuts the flange.

` Such seals are particularly convenient for manufacture by methods in which the components are assembled in position ina jig before fusion of the glass, since the flange maybe employed to locate the wire in the jig and also as a stop to locate the sleeve on the wire.

In a preferred method of manufacturing a seal according to the present invention, the metal components and the, required amount of glass are assembled vin a jig having one end closed `by a carbon surface shaped tocorrespond to the desired form of one end of the glass body, the wire or wires being fitted into one or more locating holes provided in the carbon, the jig is placed within a centrifuge in a furnace with the wires lying radially with respect to the axis of rota-tion of the centrifugeand with the carbon-closed end outwards, and the cent-rifuge is heated either directly or vindirectly within the furnace to the appropriate glass-melting temperature whilst the centrifuge is rotated at a speed suflicient for the centrifugal force generated to press the molten glass into good sealing contact with the metal components. A method` of this kind is described and claimed in copending U.S. pat-` ent application Serial No. 788,096, now Patent No. 2,992,- 513. Preferably in use of this method the wire is provided with a flange as described above, which flange rests on the carbon surface and locates the wire at the required depth in the jig, the sleeve then being assembled on the wire to rest on a glass pellet which itself rests on the flange, and the length of the sleeve and the amount of glass being chosen so that the sleeve is embedded in glass to the desired depth in the completed seal. When the seals are small a large number may be formed in la single step in a centrifuge of moderate size by this method.

Multiple seals may be formed in which two or more wires are sealed through the glass body, some or all of the wires being provided with sleeves according to the present invention. Similarly multiple seals may be formed in which a single plate, for example of metal, is provided with two or more apertures in each of which is sealed a glass body through which is sealed one or more metal wires each surrounded by a sleeve according to the invention.

sealing carried out in a single heating step in a centrifuge as described above.

In a device having a hermetically sealed envelope through which insulated electrical conductors are required to pass, for example a thermionic valve or a semiconductor device, the conductors may be sealed through the envelope by one or more seals according to any of the above aspects of the invention.

An embodiment of the invention will now be described with reference to the accompanying drawing in which FIGURE 1 is a part section through the assembled components of a seal during the process of manufacture;

FIGURE 2 is a similar part section through a completed seal; and

FIGURE 3 is a part section similar to FIG. 2 through a completed seal embodying a modied form of the invention in which two wires are sealed through the same glass portion.

Referring first to FIGURE l, a wire 1 is to be sealed through an aperture in a plate 2 by an insulating seal of matchedV glass. For example the wire and the plate` may be of copper and the glass may be copper sealing glass according to U.S. Patent No. 2,929,727. The wire 1 is formed with a flange 3, either by upsetting or by any other suitable means, for example by the use of a deformed washer according to the method described in British patent specification No. 629,742. The wire 1 and the plate 2 are assembled in a jig in which they rest the wire to rest lon the glass pellet 5.

on a graphite plate y4 lhaving a hole through which the Wire r1 passes until the flange '3 rests on the surface of the plate. A tubular pellet 5 of sintered powdered sealing glass is placed round the wire 1 and rests on the ange 3, and a sleeve `6, ,of ythe same metal as the Wire, and `of such a size as to vslide loosely yover it, is slid over A The assembly is then placed in a centrifugal sealing apparatus with the wire l arranged `radially Vand with the graphite plate 4 outwards, and yis heated to the glass melting temperature .while being rotated so as to Agenerate Ia Vcentrifugal force which presses the Vglass outwards to form the seal as vdescribed in said copending YILS. patent application No. 788,096, the completed vseal being `as shown in FIG- URE 2. i f

In one example of a seal according to the invention made by :the abovevmethod, the plate 2 was of copper, ls" thick, intendedfor attachment to the "remaining part of the metalV envelope of a semiconductor device, the wire 1 was of copper, V0.032 of an inch thick, andwas upset to form a `flange 0.1060 of an inch in diameter, and the sleeve v6 was also of copper, ofdimensions 1.067 inches outside diameter, 0.043 inch insidev diameter, and 0.105 inch long. All the copper components were lightly oxidised vand coated with borax in the usual way before assembly.

' FIG. 3 shows adouble seal, i.e. one in which two Wires .rather than `one are sealed througha single aperture in a plate by an insl-ating seal of matched glass.

' is thensealed in a centrifugal sealing apparatus as de- The sealris otherwise identical in structure and method v of manufacture to that shown in FIG. Z and correspondscribed above with reference to FIGS. 1 and 2.

A matched glasstometal seal comprising a metal Wire hermetically sealed through the glass body, and a ysingle metalsleeve closely surrounding the Wire Vand extending Ithroughfone surface of, and the greater part of .the way through, the glass body, and sealed to `the 1glass rbody on both the inner and outer surfaces of the sleeve, said metal wire having aange embedded vin the other vsurface of the t glass body, the embeddedend of the sleeve abutting said Y flange.

VReferences Cited in the le of this patent Y UNITED STATES PATENTS 'Re 22,851 Spencer Mar. l1, 1947 2,483,940 Scott 'Oot. 4, 1949 2,709,872 Slomski I-une 7, 1955 2,784,532 Grifths Mar. l12, 1957 2,859,562 Dorgelo et al Nov. 1l, 1958 2,912,794 Harvey Nov. 17, 1959 2,933,552

Schurecht n E Apr. 19, 1960 

